Technical Field
Described herein is a device comprising members in a kinematic relationship, the kinematic relationship at least partially governed by at least one magnetically induced force that introduces a force threshold that, in effect, may provide a threshold and confer a degree of hysteresis, preventing movement until a sufficiently large energizing force is applied. The effect may be further altered by use of an additional magnetically induced force interaction with at least one further member to urge or slow movement once started and/or to prevent movement once a new position is reached.
Description of the Related Art
Eddy current formation may be used in a variety of ways to adjust the speed of rotation of a member. Various apparatus exist, for example in abseiling, to control the descent of a climber or for example, in personal protective equipment scenarios to prevent an injury causing fall. Other applications that use eddy current generation are in controlling pay-out of line in trains, cable cars, zip line devices and roller coasters.
One art device is published as US2012/0055740. This device utilizes a rotor assembly with arms that move relative to the rotor. The arms themselves may be conductive or magnetic or may have conductive or magnetic members attached thereto. When a rotational force is applied to the rotor, the arms move outwards from a central axis via centrifugal force and into a magnetic (or conductive) field. As the arms move through the field, eddy currents are generated, the strength of which is dependent on the speed of rotation. As the speed of rotation reduces, the arms are drawn back towards the axis of rotation via springs and/or a reduced centrifugal force acting on the arms. This device is widely used and provides an excellent means of changing the relative speed of parts.
One aspect of the above apparatus is that there is minimal hysteresis between activation of the braking effect and non-activation. This can result is rapid on-off switching of the braking effect termed ‘chatter’. Chatter in some applications is particularly undesirable. For example, in fall safety applications,
an auto belay may be attached to a harness worn by a person in danger of a fall. If a fall occurs, the device brakes and/or stops a fall thereby preventing injury or loss of life. Chatter becomes a hindrance in fall safety use. For example, unwanted activation of the brake effect may occur when the person moves suddenly (but not a fall). False activation may result in tiring the person; the person may loose balance and fall; or false activation simply becomes a general nuisance factor. In worst cases, chatter may discourage use of the fall safety device and lead to serious injury or loss of life.
Urging or slowing movement of the arms once started in the above device via a further input may also be useful depending on the end application of the device.
As may be appreciated, providing a means of both slowing and/or fully stopping relative movement between parts in a means that may be tuned to avoid inadvertent braking and induce a tunable degree of hysteresis may be useful or at least it provides the public with a choice.
Further aspects and advantages of the device will become apparent from the ensuing description that is given by way of example only.